I was looking for a way to publish my 3D model on a website of my friend he agreed and I found Sketchfab, it's awesome but I didn't know how to upload my 3D model on the website, just on sketchfab, even though on sketchfab homepage they say publish your model anywhere including websites, can anyone help me.

You can't really upload your 3D models anywhere but you can upload to Sketchfab and embed/share anywhere else. So just upload your model to Sketchfab and use the generated embed code to embed it somewhere else.Actually pretty similar to how YouTube for example works